1. Field of the Invention
The present invention relates particularly to a hydrocracking catalyst for hydrocarbon oil, the catalyst being capable of producing middle distillates (kerosene and gas oil; kerosene-gas oil) from heavy hydrocarbons, such as vacuum gas oil (hereinafter, also referred to as “VGO”) and deasphalted oil (also referred to as “DAO”), in high yield.
2. Description of the Related Art
Hitherto, hydrotreating catalysts including zeolites in which titanium and/or zirconium is carried on (combined with) on mesopores have been used for treating bottom oil (see, for example, Japanese Unexamined Patent Application Publication Nos. 2000-334305, 2002-255537, and 2003-226519).
For example, Japanese Unexamined Patent Application Publication No. 2000-334305 discloses a hydrogenation catalyst including a hydrogenative metal carried on a catalyst support that is composed of a zeolite in which ultrafine particles composed of a titanium-group metal oxide of titania or zirconia are combined with inner surfaces of mesopores and that has an atomic ratio of aluminum to silicon in the zeolite, i.e., [Al]/[Si], of 0.01 to 0.1 (in other words, a molar ratio of SiO2 to Al2O3 (hereinafter referred to as a “SiO2/Al2O3 molar ratio” or “a silica-alumina ratio”) of 20 to 200). It is described therein that the zeolite combined with the ultrafine particles composed of the titanium-group metal oxide are prepared by bringing a raw-material zeolite with mesopores into contact with an aqueous solution of a titanium-group metal salt of titania or zirconia at a pH of 0.8 to 2, washing the zeolite with water, drying the resulting zeolite, and firing the dry zeolite at 400° C. to 600° C.
Japanese Unexamined Patent Application Publication No. 2002-255537 discloses a zeolite having a high mesopore content, an atomic ratio of aluminum to silicon, i.e., [Al]/[Si], of 0.01 to 0.2 (in other words, a silica-alumina ratio of 10 to 200), a volume percent of the mesopores each having a pore diameter of 50 to 1000 Å of 30% to 50%, a volume of the mesopores of 0.14 cc/g or more, and a proportion of tetracoordinated aluminum atoms with respect to all aluminum atoms of 25 atomic percent or more, in which metal oxide ultrafine particles of titania and/or zirconia, which is not readily reduced, are combined with inner surfaces of mesopores of the above zeolite, and a hydrotreating catalyst including a hydrogenative metal carried on a catalyst support composed of the above zeolite. The zeolite having a high mesopore content is prepared by bringing a raw-material zeolite into contact with a strongly acidic aqueous solution at a pH of 0.8 to 2, drying the zeolite at 50° C. to 200° C., and firing the dry zeolite at 350° C. to 600° C. It is described therein that it is thus possible to prepare a zeolite in which metal oxide ultrafine particles are combined with (carried on) inner surfaces of pores.
Japanese Unexamined Patent Application Publication No. 2003-226519 discloses a hydrotreating catalyst for hydrocarbon oil, the hydrotreating catalyst including a modified zeolite in which a faujasite zeolite having a crystal lattice constant of 24.28 Å or more and 24.46 Å or less contains a metal element (titanium, zirconium, or hafnium) in the 4th group of the periodic table, the modified zeolite having a metal element content of 0.1% to 10% by weight on an elemental metal basis, an Al/Si atomic ratio of 0.01 to 0.1 (in other words, a silica-alumina ratio of 20 to 200), and further containing a hydrogenative metal. It is described therein that the modified zeolite is prepared by bringing a faujasite zeolite having a crystal lattice constant of 24.28 Å to 24.46 Å into contact with an aqueous solution containing a water-soluble compound of an element in the 4th group of the periodic table under acidic conditions.
In these hydrotreating catalysts, however, the mesopores are clogged with the carried metals, and therefore these catalysts were not suited in a certain case to hydrotreating (or hydrocracking) of heavy hydrocarbon oil such as VGO and DAO.
As disclosed in WO2007/032232, hydrotreating catalyst including as a support, a Y-type zeolite containing a titanium atom incorporated into a zeolite framework (in other words, a Y-type zeolite in which aluminum atoms constituting the framework are substituted with titanium atoms) has been developed. The above zeolite can be prepared by treating a Y-type zeolite with an acidic aqueous solution containing titanium at a pH of 1.5 or less, followed by filtering, washing, and drying. Thereby, the zeolite can be made to contain titanium atoms incorporated into a zeolite framework structure without clogging mesopores. It is described that when the hydrotreating catalyst including the above zeolite as a support is applied to hydrotreating of heavy hydrocarbon oil, yields of middle distillates are improved because heavy hydrocarbon oil is readily diffused into mesopores.